Fix intermittent test failure dnssec system test

Fix intermittent test failure dnssec system test

The updatecheck-kskonly.secure zone is being used to test dynamic
updates while the KSK is offline. It ensures that the DNSKEY RRset
will retain the RRSIG record, while the updated data is being signed
with the currently active ZSK.

When walking through ZSK rollovers, ensure that the newest ZSK (ZSK3)
is published before doing the dynamic update, preventing timing
related test failures.

Also fix the test log line ($ZSK_ID3 was not yet created at the time
of logging).